EPIDEMIOLOGY MAN215 MOHAMED MB ALNOOR

CONTENTS  Definition of EPIDEMIOLOGY TIME - PLACE - PERSON  Morbidity Rates Incidence rate Attack rate Prevalence rate  Determinants of disease  Distribution of Disease

Branches, Divisions, Components Of community health (community medicine) Health Education MCH Environmental health School health Occupational health Control of communicable disease Control of noncommunicable disease

Health service administration: - Planning - Implementation - Evaluation Demography Community nutrition Biostatistics Epidemiology

الاشتقاقات Epidemiology EPI DEMOS LOGO UPON PEOPLE SCIENCE علم الناس على كاهل ( دراسة ) ( جاثم )

What is Epidemiology? Study of distribution and determinants of health-related states and events In specified populations and application of this study to control health problems.

Distribution of Disease WHEN Time WHERE Place WHO Person

Distribution of Disease WHEN Time WHERE Place WHO Person

Distribution of Disease WHEN Time WHERE Place WHO Person

Distribution of Disease Time Changing or stable Cyclic Seasonal secular

Distribution of Disease Place Geographic -Restricted/Wide spread -Coastal/inland Weather(temp., humidity, rainfall) Altitude/latitude/longitude Urban/rural

Distribution of Disease Person Age Sex Race Education Occupation behavior

Distribution of disease is quantified as morbidity rates : ? MORBIDITY Any departure ((subjective or objective )) from state of physiological or psychological well being i.e. the extent of illness, injury or disability in a defined population

Rate : a measure of the occurrence of a health event in a population group at a specified time period numerator denominator Number of events in time period Number at risk for the event :

Injury Deaths, Australia, 1992

Injury Death Rates, Australia, 1992

Why are rates useful?  Can help to identify groups with an elevated risk of disease (High-risk Groups). these groups can be studied to identify “risk factors”.

:High-risk Group A group of people in the community with a higher-than-expected likelihood Elevated probability)) for developing a particular disease, or a negative outcome. RISK The probability that an event will occur. e.g. that an individual will become ill or die within a stated period of time or age.

Risk factor: An aspect of personal behavior or lifestyle, an environmental exposure, or an inborn or inherited characteristic that is associated with an increased occurrence of disease or other health-related event or condition.

Why are rates useful?  Relate health events to a population base  This provides a basis for making valid comparisons of health events by considering the number at risk in each population  Morbidity rates are used as indicators of health INDICATORS : Measures used to predict trends, المؤشرات

Distribution of disease is quantified as morbidity rates : – Incidence rate – Attack rate – Prevalence rate

Incidence rate Number of new year cases during a year in a locality year Population at risk / year/locality = Incidence rate 1O n X  It involves only the new cases.  It measures the force of infection or disease in the community  It measures the probability that healthy people will develop disease during a specified period of time

 The numerator has to come from the population at risk for developing disease  The denominator may change over time as people develop disease  The denominator does not include persons with the disease However, in practice  in large studies, the denominator is often the mid- year population  in small studies, the denominator does not include persons with the disease Incidence rate

4/14 4

4/18 4

Example In 1429 the number of breast cancer cases reported to the cancer registry in Riyadh region was 250. The midyear population of Riyadh region was four million. Calculate the incidence rate of breast.cancer in Riyadh

Females constitute 49% of the population. incidence rate = 250 / 1,960,000 = =0.128 per 1000 female 1.28 per 10,000 female= =12.8 per 100,000 female

Attack rate Population at risk/ period Attack rate = Number of episodes during specified period x 10 n  Acute recurrent diseases, e.g. URTI, food poisoning.  Person may catch the disease more than one time.

Example: In a village of 600 persons, 120 visits to the PHCC were due to food poisoning. What is the attack rate of food poisoning in the village ?

Example: In a village of 600 persons, 1200 visits to the PHCC were due to flu. What is the attack rate of flu in the village ?

Factors affecting incidence 1- New risk factor Contraceptive pills & thromboembolism. Food additives & cancer New agent HIV & AIDS

2- Changing virulence El-Tor vibrio & cholera. H1N1 Influenza virus & influenza pandemic Mycobacterial resistance & TB

3- Changing pattern of intervention Eradication efforts & poliomyelitis Chemoprophylaxis & meningitis Environmental sanitation & filth diseases

4-Population pattern Aging & degenerative diseases & cancer

5- Reporting Increase in reporting & Early stage of surveillance &

6-Screening

7-New diagnostics

8- Changing classification Blood pressure 140/80 mmhg Vs 160/90 mmhg incidence Fasting blood sugar 126 mg/100ml Vs 140 mg/100ml incidence

9-Selective migration

Prevalence rate  Point prevalence  Period prevalence  It involves old and new cases.  It measures the disease status in the population.  It measures the disease burden.

Point prevalence: Total cases (old + new) at fixed point of time in a place total population in that place x 10 n =

prevalence: Total cases (old + new) during a period of time in a place total population in that place x 10 n = Period

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What is the period prevalence rate from Oct. 1, 1990 to Sept. 30, 1991

What is the period prevalence rate from Oct. 1, 1990 to Sept. 30,

What is the period prevalence rate from Oct. 1, 1990 to Sept. 30, /20

example MOH conducted a survey for RVF among workers in slaughterhouses in Makkah. 224 seropositive workers were identified among 6000 workers. Calculate the prevalence of RVF.

Factors affecting prevalence 1- Incidence rate & Incidence rate Prevalence rate average duration of disease 2- Disease duration = X Incidence Longer duration

3- management programs If successful and curative If only increases the survival without complete cure

4- Changing classification Blood pressure 140/80 mmhg Vs 160/90 mmhg Fasting blood sugar 126 mg/100ml Vs 140 mg/100ml Incidence

5-Selective attrition If cases of the disease travel to be treated abroad prevalence

Incidence Vs. prevalence incidence Prevalence Cure Death Migration

P No. I Time

P No. I Time

P No. I Time

P No. I Time

Determinants of Disease ( Analytical Epidemiology ) Test etiological hypotheses Identify underlying Causes Risk factors This HELPS to develop Sound health programs Interventions Policies

Aims of Epidemiology 1)To describe the distribution and magnitude of health and disease problems in human populations. 2)To identify aetiological factors( risk factors) in the pathogenesis of disease. 3)To provide the data essential for planning, implementation and evaluation of services for the prevention, control and treatment of diseases and to the setting up of priorities among these services.